Towards composite solid state laser materials

The largest recent advance in the field of solid state materials is the exponential development of the Erbium doped fibre amplifiers, the so-called EDFAs, which are already implemented in many telecommunication systems. One is already interested in the evolution of such amplifiers towards more compact devices which could be obtained through Erbium doped wave guide amplifiers. The conditions for wave guide amplifiers are first discussed showing that it will be difficult to limit the active length to less than a few tenths of a centimetre in usual glasses without having to increase the active ion concentration up to the point where self-quenching reduces prohibitively the quantum efficiency of the amplifying transition. This leads us to consider new glassy materials where the inhomogeneous linewidth of the active ions shall be reduced in order to correlatively increase the gain cross-sections. An historical review of such an approach will be presented. Then we show that composite materials of the vitroceramic type where the active rare earth ion stays only in the microcrystalline phase, provide materials with reduced inhomogeneous broadening and with crystal type optical spectra though obtained by glass technics. Evaluations of the gain cross-sections indicate increases of at least 100%. Such composite materials may so pave the way for wave guide amplifiers. (C) 1998 Elsevier Science S.A.